Getting JSON Object Result from $.post()

I'm attempting to call a web service via AJAX in a WebForms application.

My script looks something like this:

$.post('UpdateServer.asmx/ProcessItem',
     'itemId=' + $(this).text(),
     function (result) {
         alert(result);
     });
 

My web service looks something like this.

[WebService(Namespace = "http://tempuri.org/")]
 [WebServiceBinding(ConformsTo = WsiProfiles.BasicProfile1_1)]
 [System.ComponentModel.ToolboxItem(false)]
 [System.Web.Script.Services.ScriptService]
 public class UpdateServer : System.Web.Services.WebService
 {
     [WebMethod]
     public string ProcessItem(int itemId)
     {
         return new JavaScriptSerializer().Serialize(
             new { Success = true, Message = "Here I am!" });
     }
 }
 

The web method is called as expected and with the expected argument. However, the argument passed to my success function (last parameter to $.post()) is of type document and does not contain the Success and Message members that I'm expecting.

What's are the magic words so that I can get back the object I'm expecting?

EDIT

On closer inspection, I can find the data I'm looking for as follows:

result.childNodes[0].childNodes[0].data:
"{"Success":true,"Message":"Server successfully updated!"}"

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